335 research outputs found
An HST/NICMOS view of the prototypical giant HII region NGC604 in M33
We present the first high-spatial resolution near-infrared (NIR) imaging of
NGC 604, obtained with the NICMOS camera aboard the Hubble Space Telescope
(HST). These NICMOS broadband images reveal new NIR point sources, clusters,
and diffuse structures. We found an excellent spatial correlation between the
8.4 GHz radio continuum and the 2.2mu-m nebular emission. Moreover, massive
young stellar object candidates appear aligned with these radio peaks,
reinforcing the idea that those areas are star-forming regions. Three different
scaled OB associations are recognized in the NICMOS images. The brightest NIR
sources in our images have properties that suggest that they are red supergiant
stars, of which one of them was previously known. This preliminary analysis of
the NICMOS images shows the complexity of the stellar content of the NGC 604
nebula.Comment: Paper presented in the Workshop "Young massive star clusters: initial
conditions and environments" (Granada, Spain - Sept 2007). Astrophysics &
Space Science in press, 7 pages, 4 figure
A cross-calibration between Tycho-2 photometry and HST spectrophotometry
I show that Tycho-2 photometry and HST spectrophotometry are accurate and
stable enough to obtain a precise cross-calibration by analyzing a
well-calibrated sample of 256 stars observed with both Hipparcos and HST. Based
on this analysis, I obtain the following photometric zero points in the Vega
magnitude system for Tycho-2: 0.020+-0.001 (B_T-V_T), 0.078+-0.009 (B_T), and
0.058+-0.009 (V_T).Comment: 11 pages, 4 figures, to appear in Publications of the Astronomical
Society of the Pacific (June 2005 issue
Lucky Spectroscopy, an equivalent technique to Lucky Imaging. Spatially resolved spectroscopy of massive close visual binaries using the William Herschel Telescope
CONTEXT: Many massive stars have nearby companions whose presence hamper
their characterization through spectroscopy. AIMS: We want to obtain spatially
resolved spectroscopy of close massive visual binaries to derive their spectral
types. METHODS: We obtain a large number of short long-slit spectroscopic
exposures of five close binaries under good seeing conditions, select those
with the best characteristics, extract the spectra using multiple-profile
fitting, and combine the results to derive spatially separated spectra.
RESULTS: We demonstrate the usefulness of Lucky Spectroscopy by presenting the
spatially resolved spectra of the components of each system, in two cases with
separations of only ~0.3". Those are delta Ori Aa+Ab (resolved in the optical
for the first time) and sigma Ori AaAb+B (first time ever resolved). We also
spatially resolve 15 Mon AaAb+B, zeta Ori AaAb+B (both previously resolved with
GOSSS, the Galactic O-Star Spectroscopic Survey), and eta Ori AaAb+B, a system
with two spectroscopic B+B binaries and a fifth visual component. The systems
have in common that they are composed of an inner pair of slow rotators orbited
by one or more fast rotators, a characteristic that could have consequences for
the theories of massive star formation.Comment: Accepted for publication in A&A, 7 page
The Galactic O-Star Spectroscopic Survey (GOSSS). II. Bright Southern Stars
We present the second installment of GOSSS, a massive spectroscopic survey of
Galactic O stars, based on new homogeneous, high signal-to-noise ratio, R ~
2500 digital observations from both hemispheres selected from the Galactic
O-Star Catalog (GOSC). In this paper we include bright stars and other objects
drawn mostly from the first version of GOSC, all of them south of delta = -20
degrees, for a total number of 258 O stars. We also revise the northern sample
of paper I to provide the full list of spectroscopically classified Galactic O
stars complete to B = 8, bringing the total number of published GOSSS stars to
448. Extensive sequences of exceptional objects are given, including the early
Of/WN, O Iafpe, Ofc, ON/OC, Onfp, Of?p, and Oe types, as well as
double/triple-lined spectroscopic binaries. The new spectral subtype O9.2 is
also discussed. The magnitude and spatial distributions of the observed sample
are analyzed. We also present new results from OWN, a multi-epoch
high-resolution spectroscopic survey coordinated with GOSSS that is assembling
the largest sample of Galactic spectroscopic massive binaries ever attained.
The OWN data combined with additional information on spectroscopic and visual
binaries from the literature indicate that only a very small fraction (if any)
of the stars with masses above 15-20 M_Sol are born as single systems. In the
future we will publish the rest of the GOSSS survey, which is expected to
include over 1000 Galactic O stars.Comment: 110 pages, 16 figures, accepted for publication in ApJS. Some figures
have low quality due to arXiv file size limitations, alternative version
available at http://jmaiz.iaa.es/files/Sotaetal14.pd
The eccentric short-period orbit of the supergiant fast X-ray transient HD 74194 (=LM Vel)
Aims. We present the first orbital solution for the O-type supergiant star HD
74194, which is the optical counterpart of the supergiant fast X-ray transient
IGR J08408-4503. Methods. We measured the radial velocities in the optical
spectrum of HD 74194, and we determined the orbital solution for the first
time. We also analysed the complex H{\alpha} profile. Results. HD 74194 is a
binary system composed of an O-type supergiant and a compact object in a
short-period ( d) and high-eccentricity ()
orbit. The equivalent width of the H{\alpha} line is not modulated entirely
with the orbital period, but seems to vary in a superorbital period
( d) nearly 30 times longer than the orbital one.Comment: 4 pages, 6 figures, accepted for publication in A&
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